The speed of a rocket depends on thrust and the rocket's weight. Thrust is a measure of the amount of propellant used (or ejected from the rear of the rocket) and speed at which the propellant is used. Increased thrust, relative to the rocket's weight, results in greater speed.
Specific impulse is the change in momentum per unit mass for rocket fuels. Specific impulse is a measurement of how much push accumulates as fuel is consumed, or, in terms of thrust, is a rough measurement of how fast propellant is ejected from the rocket. A rocket having a high specific impulse does not require as much fuel because the rocket gets more push per amount of fuel.
Some rocket engines are variable thrust engines. Variable thrust engines do not have a constant thrust. Rather, the thrust changes as required by controlling the amount of propellants. Rockets having a variable thrust engine, therefore, can vary the propellant flow rate to meet the operational requirements while constant thrust engines cannot.
While variable thrust engines are desirable for some missions or solar system explorations, it is difficult to control the variable amount of fuel required for the desired thrust.
To increase or decrease the amount of thrust, engines are throttled. Throttling adjusts the power level of an engine within its target throttleable range, resulting in an adjustment of the amount and mixture of fuel and oxidizer reaching the engine. However, it is very difficult to control the proper mixing and amount of fuel and oxidizer over the entire target throttling range. As a result, engines tend to chug at low power levels, which leads to engine and rocket damage. In addition, the efficiency is also low at the lower power levels. Most variable thrust engines for rockets are therefore designed to operate only within a small target throttleable range.
It is desirable to design fuel injection systems which can achieve the broadest possible target throttleable range and, in particular, which can offer control of an engine at low thrust levels. High control at low thrust levels is achieved by controlling the injector inlet area while maintaining adequate pressure drop and good mixing of fuel and oxidizer.
Various attempts have been made in the prior art to control the rate of mixing and the structure of the fuel and oxidizer streams that are created when injecting fuel and oxidizer into the combustion chamber. The process of adjusting the amount of propellants into the combustion chamber is known as throttling. Traditionally the throttling of a liquid fuel engine is controlled through valves, which adjust the fuel and oxidizer flow. Control of a mixing process is particularly critical to engines.
For example, U.S. Pat. No. 3,726,088 discloses an injection element, which varies the rate of fuel into the fuel manifold by increasing and decreasing the area of the inlet slot. However, the variable inlet slot is only one physical means by which a mixing process can potentially be controlled. Injection elements have many components and geometric characteristics, which can theoretically be altered to vary the structure of the fuel and oxidizer streams to increase the level of control to optimize the mixing process.
There is an unmet need in the prior art to optimize the geometric characteristics of existing injector elements to achieve maximum efficiency of throttling speeds.
There is also a need for a method for determining specific injection area geometries to accommodate specific applications, engines and throttling requirements.